The authors applied scanning tunneling microscopy (STM) to the real-time observation of the heating-current-induced step motion on the Si(111) surface at a temperature 2 degrees C below the (1*1)-(7*7) phase transition. Each step was a monolayer in height and had a shift in the opposite direction to the heating current direction or electric field. Step shifting was terminated at certain positions. Three monolayer steps moved around the terminated positions. When another step was getting closer to these three steps, the latter had the tendency to stop and became centers for step bunching. In order to explain these behaviours, the authors propose an electric-field-induced model together with the presence of pinning centers such as impurities, stresses, or adsorbates. This electric-field-induced step shifting can be applied to control the surface structures on an atomic scale.
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